Pneumatic fastener driving apparatus



p 1969 E. FISHER PNEUMATIC FASTENER DRIVING APPARATUS 3 Sheets-Sheet 1Filed June 28, 1966 s w mm m 6 Mn A Q M W a a 2 r; X f J M 1 .P a m fl nW WWW, w a fo fv fl/ IH Qu w wflfi w 74 /L. UPI w MU -1 N Sept. 16, 1969E. l. FISHER 3,467,294

PNEUMATIC FASTENEH DRIVING APPARATUS Filed June 28, 1966 FT W M 3Sheets-Sheet BY %WQ %M ATTORNEYS Sept. 16, 1969 E. l. FISHER 3,467,294

PNEUMATIC FASTENER DRIVING APPARATUS Filed June 28, 1966 3 Sheets-Sheetl- BY W ATTORNEYS United States Patent PNEUMATIC FASTENER DRIVINGAPPARATUS Edward I. Fisher, Westerly, R.I., assignor to Bostitch,

Incorporated, East Greenwich, R.I., a corporation of Rhode Island FiledJune 28, 1966, Ser. No. 561,095 Int. Cl. 1321i 15/28; B27f 7/06; BZSc/02 U.S. Cl. 2278 6 Claims ABSTRACT OF THE DISCLOSURE A pneumaticallyactuated fastener driving apparatus embodying a housing having adifferential cylinder receiving a differential driving piston, thedriving piston having a fastener driving element connected therewith fordriving staples and the like fed to a drive track from a magazineassembly. The apparatus includes a trigger actuated control valve forcommunicating a source of air under pressure with the drive piston tomove the latter through a drive stroke. The drive piston is providedwith a relatively sharp upwardly extending rim which engages a resilientpad when the drive piston is in its uppermost position, the engagementof the rim with the pad serving to delay the initiation of the drivestroke until the air under pressure communicated with the drive pistonincreases to a value substantially equal to the pressure of the source.The differential cylinder is provided with an opening in the wall whichserves to communicate the air under pressure which moves the pistonthrough the drive stroke to the differential chamber when the pistonreaches a position adjacent the end of its drive stroke so as to chargethe differential chamber with air under pressure operable to effect thereturn stroke of the piston. During the return stroke, the air above thedrive piston is discharged to atmosphere under the control of thetrigger actuated valve through the bottom of the differential cylinderso as to prevent a suction action therein. A contact trip element ismounted on the apparatus adjacent the nosepiece for movement from aninoperative position into an operative position in response to themovement of the device against a workpiece. The trigger is pivotallycarried by a structure movable with the contact trip element and isarranged so as to actuate the control valve only in response tosimultaneous movement of the contact trip assembly into its operativeposition with a manual actuation of the trigger or when both movementsare sequentially performed in either order. The housing is provided withabutments including ribs on opposite sides of the trigger to preventmanual movement of the trigger into a position to actuate the controlvalve when the contact trip is in its inoperative position.

This invention relates to fastener driving apparatus and moreparticularly to fastener driving apparatus of the type actuated by airunder pressure.

An object of the present invention is the provision of a fastenerdriving apparatus of the type described which is characterized bysimplicity of construction involving a minimum number of operative partswhich can be economically fabricated and assembled, rendering theapparatus capable of economic construction while still maintainingefficient operation and low maintenance.

Another object of the present invention is the provision of a fastenerdriving apparatus of the type described having improved means forinitially charging and maintaining the space between the piston heads ofa differential piston assembly charged with air under pressure for thepurpose of returning the piston assembly after each driving stroke andhence to supply adequate lubrication there- 3,467,294 Patented Sept. 16,1969 to by means of a lubricant contained within the air chargedtherein.

Another object of the present invention is the provision of a fastenerdriving apparatus of the type described having improved means forpreventing the suction of air and hence dirt and other foreign materialinto the interior working parts of the apparatus through the dischargeopening of the cylinder during the return movement of the pistonassembly therein.

Still another object of the present invention is the provision of afastener driving apparatus of the type described having improved meansfor delaying the initial driving stroke of the piston assembly untilsuch time as the air under pressure available to effect the drivingstroke of the piston assembly has built up to a pressure substantiallyequal to the supply or reservoir pressure so as to insure a rapid andeffective driving stroke.

Still another object of the present invention is the provision of afastener driving apparatus of the type described having an improvedvalve mechanism therein for effecting the driving and return strokes ofthe piston assembly.

A still further object of the present invention is the provision of afastener driving apparatus of the type described having improvedinterlock means for permitting drag firing and bump firing of theapparatus and single firing of the apparatus only when both the triggermember has been manually depressed and the apparatus has been moved intowork engaging relation.

These and other objects of the present invention will become moreapparent during the course of the following detailed description andappended claims.

The invention may best be understood with reference to the accompanyingdrawings wherein an illustrative embodiment is shown.

In the drawings:

FIGURE 1 is a perspective view of a fastener driving apparatus embodyingthe principles of the present invention;

FIGURE 2 is an enlarged fragmentary sectional view taken along the line22 of FIGURE 1 showing the position of the parts in their normallybiased inoperative position;

FIGURE 3 is a view similar to FIGURE 2 showing the parts in theiroperative fastener driven position;

FIGURE 4 is a fragmentary sectional view taken along the line 4-4 ofFIGURE 2;

FIGURE 5 is a fragmentary front elevational view showing the workengaging member of the apparatus; and

FIGURE 6 is a fragmentary sectional view taken along the line 6- 6 ofFIGURE 5.

Referring now more particularly to FIGURE 1 of the drawings, there isshown therein a fastener driving apparatus, generally indicated at 10,embodying the principles of the present invention. The apparatusincludes a housing, generally indicated at 12, including a base portion14 shaped to receive a fastener magazine assembly, generally indicatedat 16. The magazine assembly may be of any suitable construction and isconventional in operation. The details of construction thereof form nopart of the present invention.

Fixedly mounted on the housing 12, as by bolts 18 or the like, is a nosepiece 20 having a fastener drive track or passage 22 formed thereinwithin which the leading fastener of a fastener stick mounted within themagazine assembly 16 is adapted to be engaged in conventional fashion.

As best shown in FIGURES 2 and 3, the apparatus 10 includes apneumatically actuated driving system, generally indicated at 24,mounted within the housing 12 to drive the leading fastener containedwithin the magazine assembly 16 outwardly of the guide track and into awork piece. The driving system 24 is of a type which may either be dragfired or bump fired and to this end includes a manually actuatabletrigger member 26 and a work engaging member 28, both of which must beactuated to operate the driving system 24 to drive a fastener into thework piece.

The driving system 24 includes, in general, a piston assembly 30 mountedwithin an elongated portion 32 of the housing 12 disposed inlongitudinal alignment with guide track 22. The piston assembly 30 ismounted within the housing portion 32 for longitudinal reciprocatingmovement including a driving stroke and a return stroke and has a driverblade member 34 connected for movement therewith which, during thedriving stroke of the piston assembly 30, will engage the fastenerwithin the guide track 22 and move the same into the work piece.

The piston assembly 30 is reciprocated by air under pressure from asuitable source (not shown) which is communiacted with an inlet pressurereservoir or chamber 36 formed in a hollow handle portion 38 of thehousing extending outwardly from the end of the housing portion 32remote from the nose piece 20. Preferably, the outer end of the handleportion 38 is interconnected with the base portion 14 as by a connectingportion 40, so that with this construction the main housing of theapparatus is formed from a single casting.

Mounted within the housing between the inlet pressure chamber 36 and thepiston assembly 30 is a control valve mechanism, generally indicated at42, which serves to control the communication and discharge of air underpressure to the piston assembly to effect the reciprocatory movementthereof. The valve mechanism 42 is adapted to be actuated by theaforesaid cooperative action of the trigger member 26 and work engagingmember 28 through an interlocking structure, generally indicated at 44.

As best shown in FIGURE 2, the piston assembly 30 is of the differentialpressure type and includes first and second axially spaced piston heads46 and 48 rigidly interconnected in spaced relation by a central stemportion 50. The first piston head 46 is of a diameter size greater thanthe diameter size of the second piston head 48 and is mounted forlongitudinal reciprocatory movement within a first cylindrical chamber52. The second piston head 48 is mounted for longitudinal reciprocatorymovement within a second cylindrical chamber 54, the second chamber 54being formed in the housing 12 as by a bore or the like, with the firstchamber 52 constituting a counterbore therein defining aninterconnecting annular shoulder 56 therebetween.

The piston heads 46 and 48 are sealed within their respective chambers52 and 54 by any suitable means, such as annular sealing members 58 and60 of conventional O-ring construction, mounted within annular grooves62 and 63 formed in the outer periphery of the piston heads 46 and 48,respectively. It will be understood that in accordance with conventionalpractice, the annular sealing members 58 and 60 are slidably sealinglyengaged with the interior peripheral surface of the chambers 52 and 54,respectively.

An important feature of the present invention resides in the structurefor charging the space between the piston heads 46 and 48 with air underpressure during each driving stroke of the piston assembly to effect thereturn stroke of the piston assembly and to maintain a fresh supply oflubricating oil within this space. In accordance with the principles ofthe present invention, this function is achieved simply by cutting anarcuate groove 64 in the wall of the first cylindrical chamber 52 at aposition adjacent the shoulder 56 so that when the annular sealingmember 58 is moved into a position intermediate the ends of the groove64 the pressure acting on the piston head 46 will be bypassed around thepiston head and into the space between the piston heads.

The driver blade member 34 is connected with the second piston head 48for movement therewith by any suitable means. As shown, the secondpiston head 48 is of generally hollow construction opening in adirection facing toward the nose piece 20 and has an insert 66 ofplastic material mounted therein which is provided with an axiallyextending slot 68 and a transversely extending aperture 70 intersectingthe slot 68. The adjacent end of the driver blade member 34 is disposedwithin the slot 68 and has an aperture 72 formed therein for receiving asecuring rod or pin 74 disposed in the transverse aperture 70 within theinsert 66.

The portion of the housing 12 between the drive track 22 and theadjacent end of the second chamber 54 is formed with an enlarged Opening76 within which the opposite end portion of the drive blade is mountedand through which the adjacent end of the chamber 54 is communicatedwith the atmosphere. Disposed within the adjacent end of the chamber 54is a bumper ring 78 of rubber or other suitable resilient material, thering being of generally octagonal configuration in cross section, asshown. The bumper ring 78 serves to receive the piston head 48 duringthe driving stroke of the piston assembly and to cushion the end of thismovement. In order to prevent the engagement of the piston head with thebumper from sealing the adjacent periphery of the chamber 54, aplurality of radially extending grooves 79 are formed in the uppersurface of the bumper ring.

As best shown in FIGURES 2 and 3, the control valve mechanism 42 ismounted within a bore 80 formed in the housing 12 in parallel relationto the cylindrical chambers 52 and 54. A counterbore 82 is formed withinthe outer end of the bore 80 and receives therein a sleeve insert 84.The sleeve insert has a lateral inlet opening 86 formed in the outer endportion thereof which communicates with a passage 88 formed in thehousing 12 in communication with the pressure reservoir or chamber 36.As shown, the handle portion of the housing 12, defining the oppositeend of the chamber 36, is provided with a threaded inlet opening 90 toreceive one end of a hose fitting (not shown) which serves to connectthe apparatus 12 with a source of air under pressure (not shown).

The insert sleeve 84 is also formed with a lateral outlet opening 92which faces in a direction opposite from the opening 86 and communicateswith one end of an inlet passage 94 formed in the housing, the oppositeend of which communicates with a lateral opening 96 communicating withthe adjacent end of the first cylindrical chamber 52. As shown, theinner end of the insert 84 is sealed within the counterbore, as by anannular seal 98, disposed on one side of the passage 94 and an annularseal 100 serves to seal the insert 84 within the counterbore between theopenings 86 and 92. Formed on the inner periphery of the insert 84between the openings 86 and 92 is an inwardly facing frusto-conicalvalve seat 102 which is adapted to be engaged by an exteriorfrusto-conical surface 104 formed on one end of a spool valve member 106mounted within the bore 80 and the inner end portion of the insert 84.

Formed on the exterior periphery of the spool valve member 106 adjacentthe frusto-conical surface 104 is a cylindrical control portion 108which is adapted to sealingly engage within a cooperating cylindricalsurface 110 formed on the interior inner portion of the insert 84. Theexterior periphery of the spool valve member is also formed with anannular groove 112, adjacent the control portion 108, having an axialextent sufficient to provide communication between the opening 92 andthe bore 80 when the frusto-conical surface 104 is disposed inengagement with the spool valve member 106. The outer end of the bore80, adjacent the inner end of the insert 84, has one end of a dischargepassage 114 communicating therewith, the opposite end of whichcommunicates with the chamber 54 at a position adjacent the end thereofwithin which the bumper ring 78 is mounted.

The communication of the discharge passage 114 with the chamber 54 atthe position indicated is an important feature of the present inventionsince, by this structural arrangement, air under pressure will bedischarged into the second cylindrical chamber 54 adjacent the dischargeopening 76 therein at a time when the second piston head is moving awayfrom the opening, which movement, in the absence of the introduction ofair under pressure from the discharge passage 114, would tend to createa suction of air through the opening 76 tending to draw dirt and otherforeign matter into the working parts of the driving system.

The end portion of the spool valve member 106 opposite from thefrusto-conical surface 104 is mounted within the bore 80 and has anannular groove 116 formed in the exterior periphery thereof within whichan annular seal 118 is mounted. The seal 118 slidably sealingly engagesthe wall of the bore 80 and defines a pilot pressure chamber within theinner end of the bore 80. The pilot pressure chamber is communicatedwith the atmosphere by means of a central opening 120. Disposed insurrounding relation to the opening 120 adjacent the inner side thereofis an annular valve seat 122 which, as shown, is in the form of anO-ring of resilient material or the like.

The valve seat 122 is adapted to be engaged by a frustoconical surface124 formed on the exterior periphery of a trigger valve member 126.Valve member 126 is provided with a cylindrical control portion 128 onthe exterior periphery thereof adjacent the frusto-conical surface 124for movement within a cylindrical interior peripheral portion 130 of thespool valve member. The relative diameter sizes of the exterior controlportion 128, the trigger valve member 126, and the interior cylindricalportion 130 of the spool valve 106 are such as to permit a slight airleakage thereby.

The trigger valve member 126 includes a sleeve-like guide portion 132disposed within the cylindrical portion 130 of the spool valve member106 having an exterior diameter size somewhat less than the cylindricalcontrol surface 128. The interior of the sleeve portion 132 receives oneend of a compression coil spring 134, the opposite end of which engageswithin the end of the spool valve member adjacent the inner end of thecylindrical portion 130. The spring 134 thus serves to resiliently biasthe valve members 106 and 126 in a direction away from each other sothat they are in engagement with the valve seats 102 and 122,respectively, as shown in FIGURE 2.

In order to actuate the valve mechanism 42 to initiate the drivingstroke of the piston assembly 30, trigger valve member 126 is providedwith a stem portion 136 which extends outwardly of the opening 120 andhas its outer end shaped for engagement by an actuating surface 138formed on the center portion of the trigger member 26.

The interlocking structure 44, which serves to mount the trigger member26 on the housing 12 in a position to permit the trigger actuatingsurface 138 to engage the trigger valve stem portion 136, includes anelongated motion transmitting member 140 of generally U-shapedconfiguration in cross section. The member 140 is mounted forlongitudinal reciprocating movement on the exterior of the housingportion 32 at a position adjacent the valve mechanism 42 and between apair of transversely spaced rib portions 142, forming an integral partof the housing 12. As shown, a pin 144 is mounted between the ribportions 142 and serves to retain the motion transmitting member 140 insliding engagement with the adjacent surface of the housing portion 32.The end of the member 140 adjacent the trigger 26 has its bight or webportion cut out to receive the adjacent end of the trigger memberbetween the leg portions thereof. The trigger member is pivotallyconnected to the motion transmitting member 140, as by a pivot pin 146.

The opposite end of the motion transmitting member 140 has a pair ofparallel leg portions 148 extending transversely outwardly therefrom ingenerally perpendicular relation within a pair of side grooves orrecesses 150 formed in the adjacent portion of the housing. The freeends of the leg portions 148 are adapted to engage within a pair of sideopening notches 152 formed within one end of the work engaging member28.

As best shown in FIGURES 2, 3 and 5, the drive track 22 is defined byone surface of the work engaging member 28 and by a longitudinallyextending recess formed in one surface of the nose piece 20. The workengaging member is mounted for longitudinal reciprocatory movement onthe nose piece 20, by any suitable means, and, as shown, the nose pieceis provided with a pair of transversely spaced guide portions 154 havingopposed longitudinally extending grooves 156 formed therein whichslidably receive the opposite edge portions of the member 28.

The work engaging member 28 is thus mounted for longitudinalreciprocatory movement with the motion transmitting member 140 andincludes an outer end portion 160 which is adapted to extend outwardlyof a work engaging portion 158 of the nose piece 20 when the member 28is disposed in its normally biased position, as shown in FIGURE 2. Thisposition is determined by engagement of the adjacent end of the member140 with the base portion 14 of the housing. The contact trip member 28is normally maintained in such position by suitable spring means such asa tension spring 162 connected between a pin in 164, extending acrossthe leg portions of the member 140 adjacent pin 144 and a pin 166 fixedto the adjacent base portion 14 of the housing 12.

The end portion of the trigger member 26 opposite from the pivot pin 146is formed with a concavely arcuate finger-engaging surface 168 whichfaces in a direction opposite from the stem-engaging surface 138. Whenthe trigger member 26 is disposed in its inoperative position, as shownin FIGURE 2, the finger-engaging surface 168 is disposed in spacedrelation to generally coextensive finger-engaging surfaces 170 formed onthe rib portions 142 of the housing 12. The trigger member 26 alsoincludes an abutment surface 172 facing in a direction toward theadjacent housing portion 38 and disposed in spaced relation thereto whenthe trigger member is in its inoperative position a distance generallyequal to the spacing between the finger-engaging surfaces 168 and 170.The trigger abutment surface 172 is adapted to engage an abutmentsurface 174 on the adjacent portion of the housing when the triggermember 26 is manually depressed.

It will be noted that the outer ends of the first cylindrical chamber 52and the outer end of the sleeve insert 84 are open at the adjacentportion of the housing. A cover member 176 is provided for the purposeof closing this open portion of the housing. As shown, a gasket 177 ismounted between the cover member and adjacent portion of the housing anda series of bolts 178 extend through the cover member and are threadedlyengaged with the housing to retain the cover member fixedly there- Asbest shown in FIGURES 2 and 3, the interior portion of the cover memberadjacent the cylindrical chamber 52 is recessed, as indicated at 180, tofixedly receive therein a pad 182 of resilient material. Preferably, thepad is formed of a synthetic rubber having a durometer of from 50 to 60,55 durometer being preferred. The pad 182 forms a part of a fluidpressure actuated timing means which constitutes an important feature ofthe present invention, serving to delay the driving stroke of the pistonassembly for a time suflicient to permit the buildup of pressuresubstantially to the pressure of the source so as to effect a rapidinitial driving stroke of the piston assembly.

The upper end of the piston head 46 is shaped to cooperate with the pad182 and forms a cooperating part of the timing means. To this end, theouter periphery of the piston head 46 is formed with a relatively sharpouter annular edge 184 as, for example, an edge having a radius of theorder of 0.005 inch. The annular edge 184 is dimensioned as closed aspossible to the dimension of the piston head 46 so as to define amaximum area when in engagement with the pad 182. The outer end surfaceof the piston head 46 includes an outer annular frustoconical rimsurface 186 which merges at its outer periphery with the edge 184 and atits inner periphery with an annular recess 188 formed in the centralportion of the piston head. It will be noted that the recess 188 and rimsurface 186 define with the pad 182 and annular edge 184, when thelatter are in engagement, a timing chamber into which air under pressurewithin the lateral opening 96 leaks between the annular edge 184 and thepad 182 to initiate the driving stroke of the piston assembly.

OPERATION As noted above, the apparatus of the present invention iscapable of drag firing and bump firing by virtue of the interlockstructure 44. This structure permits single firing of the apparatus onlyafter the work engaging member 28 has been moved from its normallybiased position, as shown in FIGURE 2, into its operative or secondposition, as shown in FIGURE 3, and the trigger member 26 is manuallydepressed from its normally biased position, as shown in FIGURE 2, toits operative position, as shown in FIGURE 3.

With reference to FIGURE 2, it will be noted that tension spring 162serves to retain the outer end portion 160 of the work engaging member28 beyond the adjacent end portion 158 of the nose piece 20. The weightof the trigger member 26 maintains it in a normally biased position, asshown in FIGURE 2. If the operator depresses the trigger member 26Without engaging the member 28 with the work piece, trigger member 26will merely move into the dotted line position shown in FIGURE 2 whereinabutment surfaces 172 and 174 engage one another without the surface 138engaging the valve stem portion 136. It will be noted that in the dottedline position, the trigger member is disposed substantially entirelywithin the rib portions 142 so that further efforts by the operator todepress the trigger member will simply result in digital pressure beingapplied to the finger engaging surfaces 170.

With reference to FIGURE 3, it will be noted that the engagement of themember 28 with the work piece to effect movement thereof into itsoperative position, as shown in FIGURE 3, without a manual depression ofthe trigger member 26 will result in the trigger member assuming theposition shown in dotted lines wherein valve stem portion 136 is notengaged. Thus, it is not until both members 26 and 28 are moved intotheir operative positions, as shown in full lines in FIGURE 3, that thedriving system 24 is actuated. The trigger member is thus movable intofour positions, namely: a first normally biased position, as shown infull lines in FIGURE 2, wherein the work engaging member 28 is disposedin its inoperative position; a second position wherein the work engagingmember 28 has been moved into its operative position but the triggermember has not been manually moved, as shown in dotted lines in FIGURE3; a third position wherein the trigger member has been manually movedbut the work engaging member has not been moved into its operativeposition, as shown in dotted lines in FIG- URE 2; and finally, a fourthoperative position wherein the work engaging member has been moved intoits operative position and the trigger member manually moved into itsoperative position, as shown in full lines in FIGURE 3.

It will be noted that movement of the trigger member into any positionother than its operative position will not result in the engagement ofthe actuating surface 138 thereof with the stem portion 136 of thetrigger valve member 126, so that the latter will remain in its closedposition. It is only when the trigger member 26 is moved into itsoperative position that the actuating surface 138 will engage and movethe stem portion 136 of the trigger valve member into its openedposition to initiate the operation of the driving system 24.

The arrangement of the interlock structure 44 is such that the triggermember 26 can be moved into its operative position in three distinctways. First, by simultaneous movement of the work engaging member 28into its operative position with a manual movement of the trigger member26; second, by movement of the work engaging member 28 into itsoperative position while the trigger member 26 is maintained in itsthird position; or third, by manually engaged movement of the triggermember 26 while the work engaging member 28 is maintained in itsoperative position. The capability of effecting movement of the triggermember 26 into its operative position by the last two procedures makespossible bump firing and drag firing, respectively.

Bump firing would be accomplished by continuously manually depressingthe trigger member 26 and bumping or lifting the entire apparatussuccessively into engagement with the work piece so as to cycle the workengaging member 28 by each engagement of the work piece. Drag firingwould be accomplished by the operator maintaining a pressure on thehandle portion 38 to keep the work engaging member 28 in contact withthe work piece and then successively depressing the trigger member 26while the apparatus is moved along the surface of the work piece.

The valve mechanism 42 is operable to efiect a movement of the pistonassembly 30 from the fastener receiving position, shown in FIGURE 2, tothe fastener driven position, shown in FIGURE 3, in response to themovement of the trigger member 26 into its operative position, as shownin full lines in FIGURE 3 in the following manner. It will be noted thatwhen the valve mechanism 42 is in its inoperative position, as shown inFIGURE 2, the valve members 106 and 126 are disposed in their outerlimiting positions wherein the firustoconical surface 104 of the spoolvalve member 106 is in engagement with valve seat 102, and thefrusto-conical surface 124 of the valve member 126 is in engagement withthe valve seat 122. Consequently, air under pressure within thereservoir 36 is prevented from entering the inlet passage 94, but isadmitted to the pilot pressure chamber defined by the bore through theinterior surface 130 of the spool valve member 106. The pressure withinthe pilot chamber serves to maintain the spool valve member 106 in itsclosed position since the surface area thereof communicating with thepilot pressure chamber is greater than the surface area communicatingwith the reservoir chamber 36. In addition, spring 134 aids inmaintaining the spool valve member 106 in its closed position, as wellas the trigger valve member 126 in its closed position.

When the trigger member 26 is moved into its operative position,actuating surface 138 will engage the stern portion 136 of the valvemember 126 moving the latter inwardly of the spool valve member 106.During this movement, the frusto-conical surface 124 is moved away fromthe valve seat 122 thus discharging the pilot pressure chamber toatmosphere through the opening 120. As soon as the pilot pressure isrelieved to the atmosphere, the pressure within the reservoir chamber 36acting on the adjacent end of the spool valve member will effectmovement of the latter away from the valve seat 102. During thismovement, the cylindrical control portion 128 of the trigger valvemember 126 engages within the cylindrical interior peripheral portion130 of the spool valve member 106 preventing substantial passage of airunder pressure through the spool valve member. In addition, the controlportion 108 of the spool valve moves into closing relation within thecylindrical surface preventing communication of the air under pressurewith the discharge passage 114. Consequently, as the spool valve member106 moves away from its seat 102, the pressure within the reservoir 36will pass into the inlet lateral opening 96.

The pressure communicated with the lateral opening 96, however, does notimmediately act upon the piston assembly 30 by virtue of the engagementof the annular edge 184 with the pad 182, since there is substantiallyno surface area upon which the pressure can act to effect movement ofthe piston assembly. However, as the pressure within the opening 96builds up, leakage will occcur between the annular edge 184 and the pad182 until sufficient pressure is built up within the timing chamberdefined by the recess 188 and rim surface 186 to overcome thedifferential component resulting from the pressure within the cylinder52 between the differential piston heads 46 and 48.

Due to the delayed action of the edge to pad engagement, the pressurewithin the lateral opening 86 has time to build up substantially to thereservoir pressure before any movement of the piston assembly 30 occurs.Thus, since substantially full reservoir pressure is available to thefull surface area of the piston head 46 after the initial movementoccurs, this initial movement will be very rapid, thus resulting in arapid movement of the piston assembly 30 from the fastener receivingposition, shown in FIGURE 2 to the fastener driven position, shown inFIGURE 3.

During this movement, the driver blade member 34 is moved through thefastener drive passage 22 to engage a fastener disposed therein and movethe same outwardly into the work piece with a rapid and forceful action.

During the movement of the piston assembly 30 from its fastenerreceiving position to its fastener driven position, the air within thesecond cylinder 54 will be discharged to the atmosphere through opening76. When the piston assembly reaches a position adjacent the fastenerdriven position, the annular seal 58 will contact the arcuate groove 64permitting the air under pressure acting on the first piston head 46 tobypass the piston head and enter the space between the piston heads 46and 48, thus charging the same with air under pressure.

When the trigger member is moved out of its operative position, thetrigger valve member 126, through the action of spring 134 will moveinto closing engagement with the valve seat 122 thus sealing the pilotpressure chamber from the atmosphere. Air under pressure from thereservoir then leaks by the cylindrical control surface 128 to chargethe pilot pressure chamber with air under pressure until it reaches avalue sufficient to effect movement of the spool valve member 106 towardits seat 102 in conjunction with the action of spring 134. During thismovement, control portion 108 of the spool valve member 106 moves out ofclosing relation with the cylindrical opening 110 thus communicating theinlet passage 94 with the discharge passage 114 past the annular groove112. Immediately following the communication of the inlet passage 94With the discharge passage 114, the frusto-conical surface 104 of thespool valve will engage the valve seat 102 closing off air underpressure in the reservoir 1%. As the pressure within the chamber 52 israpidly decreased, the air under pressure within the space between thepiston heads acts to effect a movement of the piston assembly from itsfastener driven position to its fastener receiving position.

During this movement the air Within the first cylindrical chamber 52 isdischarged through the inlet opening 94, past the annular groove 112,through the discharge passage 114, and into the second cylindricalchamber 54 adjacent the opening 76. By discharging, in this fashion, theair under pressure, which is communicated with the piston assembly 30 toeffect the driving movement thereof, there is sufficient air underpressure introduced into the second cylindrical chamber 54 to preventthe creation of a negative pressure therein during the movement of thepiston assembly 30 into its fastener receiving position. The preventionof a negative pressure within the chamber 54 is important since itprevents suction of dirt and other forchamber 94 and the eign materialthrough the opening 76 and into the interior working parts of thedriving system 24. Thus, with the present arrangement there will be nodirt or other material drawn into the mechanism and maintenance problemsare reduced to a minimum.

It thus will be seen that the objects of this invention have been fullyand effectively accomplished. It will be realized, however, that theforegoing specific embodiment has been shown and described only for thepurpose of illustrating the principles of this invention and is subjectto extensive change without departure from such principles. Therefore,this invention includes all modifications encompassed within the spiritand scope of the following claims.

What is claimed is:

1. Pneumatically actuated fastener driving apparatus comprising ahousing defining cylindrical chamber means,

piston means mounted within said chamber means for axial reciprocatingmovement,

valve means for controlling the communication of a source of air underpressure with one end of said chamber means to effect movement of saidpiston means from a fastener receiving position to a fastener drivenposition and for isolating said One end of said chamber means from thesource of air under pressure and permitting the air under pressurecommunicated therewith to discharge to the atmosphere during movement ofsaid piston means from said fastener driven position to said fastenerreceiving position,

fastener driving means connected with said piston means for movementtherewith to drive a fastener in response to the movement of said pistonmeans from said fastener receiving position to said fastener drivenposition, and

means for delaying the movement of said piston means out of saidfastener receiving position for a period sufficient to permit the airunder pressure adjacent said one end of said chamber means to build upsubstantially to the pressure of the source so that the built uppressure will effect a rapid initial movement of said piston means outof said fastener receiving position, said delaying means comprising apad of rubber-like material fixedly carried by said housing adjacentsaid one end of said chamber means,

a fixed annular portion on said piston means facing in a directiontoward said pad having a relatively sharp annular pad engaging edge of adiameter substantially equal to the diameter of said piston means, saidfixed portion defining with said pad when said annular edges is inengagement therewith a chamber into which the air under pressureadjacent said one end of said chamber means leaks between said annularedge and said pad to initiate the movement of said piston means out ofsaid fastener receiving position.

2. Apparatus for driving a fastener into a work piece when in workengaging relation thereto comprising a housing having means defining afastener drive passage,

fastener driving means carried by said housing for movement between afastener receiving position and a fastener driven position and operableduring movement from said fastener receiving position into said fastenerdriven position to move through said fastener drive passage to engage afastener therein and move the same outwardly into a work piece,

a work engaging structural assembly carried by said housing for movementfrom a normally biased first position into a second position in responseto the movement of said apparatus into work engaging relation,

a trigger member pivotally carried by said work engaging assembly formovement from a normally biased first position into a second position inresponse to the movement of said work engaging assembly from its firstposition into its second position,

first and second annular seal means carried by said first and secondpiston heads and slidably, sealingly engaging said first and secondcylindrical chambers, respectively,

valve means for controlling the communication of a said trigger memberhaving a finger engaging sursource of air under pressure with theopposite end face digitally engageable to move said trigger memof saidfirst chamber to effect movement of said pisber from the first andsecond positions thereof into ton assembly from a fastener receivingposition third and fourth positions, respectively, wherein said firstpiston head is disposed adjacent abutment means fixed with respect tosaid housing and the opposite end of said first chamber to a fastenerdisposed in a position to prevent digitally engage driven positionwherein said first piston head is dis movement of said trigger memberinto said fourth posed adjacent said one end of said first chamberposition when said work engaging assembly is disand for isolating theopposite end of said first champosed in its first position, and ber fromthe source of air under pressure and permeans Carried y said housingoperable to effect move- 15 mitting the air under pressure communicatedtherement of said fastener driving means from said faswith to dischargeto the atmosphere during movetener receiving position into said fastenerdriven pot f s id i to assembly from said fastener sition ill fesponsst0 the movement of said trigger driven position to said fastenerreceiving position, msmbsr into said fourth Position only, eitherfastener driving means connected with said piston asy simultaneousmQVemsIlt of said Work engaging sembly for movement therewith to drive afastener assembly into its second Position With digitaiiy in response tothe movement of said piston assembly e s movement of Said trigger memberinto its from said fastener receiving position to said fastener fourthposition, (2) by movement of said work end i i i gaging assembly intoits second Position While said said housing having groove means formedin said first trigger member is digitaiiy maintained in its thirdchamber adjacent said one end thereof in a position Position, 9F ydigitally engaged movement of such that said first annular seal means isdisposed said tfiggsl' member into its fourth Position Whileintermediate the ends thereof when said piston assaid Work engagingassembly is maintained in its sembly is in said fastener driven positionto thereby second Position communicate the air under pressure acting tomove 3. Apparatus as dsiined in Claim 2 wherein Said Work said pistonassembly toward said fastener driven poerlgaging asssmbiy mprises sitionwith the space between said annular seal a Plate-like Work engagingmember mounted for means and charge the latter with air under pressurecipl'ocating moyemsllt in a Position to defim one so that uponcommunication of the opposite end of Su a e Of said fastener drivePassage, said first chamber with the atmosphere the air under a motiontransmitting membal' mounted 011 Said hous pressure charged into saidspace will effect movement ing for reciprocating movement, said motiontrans of said piston assembly from said fastener driven pomitting memberincluding sition to said fastener receiving position, an BiOIlgatedPorti0n pivotally receiving at one end means for delaying the movementof said piston assemthsreof said trigger member and bly out of saidfastener receiving position for a a pair of leg portions extendinglaterally outwardly 40 period ffi i t to permit the air pressum dj fromthe opposite end thereof, the free ends of said the opposite end of Saidfirst chamber to build up portions being connected Wlth Sald Work engag'substantially to the pressure of the source so that the p member andbuilt up pressure will effect a rapid initial movement spmigmeans forreslhenfly urgmg Sald nionon transof said piston assembly out of saidfastener receivmitting member and sald work engaging member g positionInto positions corrFspondmg to the normally blased said delaying meanscomprising a pad of rubber-like first position of said work engaglngassembly. fi d1 d b h m the 4. Apparatus as defined in claim 3 whereinsaid trigmaterial Xe f y Ousmg a lace ger member is pivotally mounted atone of its ends to opposlteqndo sa1d first ham I the one end of theelongated portion of said motion transr0 3 fixed Portion P Said plstqnhead f m dlrec' mitting member. 0 tron toward said pad having arelauvelysharpen- 5, Apparatus as defined in claim 2 wherein nular pad engagingedge of a dlameter substantially said trigger member is pivotallymounted at one of its equal to the diameter of said first piston head,

ends to said work engaging assembly, and said fixed portion definingwith said pad when said said abutment means includes annular edge is inengagement therewith a chamber a surface on said housing for engaging tpP 0 into which the air under pressure adjacent the one site end P ofsaid trigger member h end of said chamber means leaks between saidansaid tfiggsl' member is moved into said third nular edge and said padto initiate the movement of Position and said piston assembly out ofsaid fastener receiving a pair of fixed rib portions on said housing onposition opposite sides of said trigger shgpefd todprevent ReferencesCited di ital movement of the one en 0 sai trigger mgmber into saidfourth position when the lat- UNITED STATES PATENTS teri disposed insaid third position- 2,888,679 6/1959 Peterssen et al 227 13o 6.Pneumatically actuated fastener driving apparatus 3,040,709 6/1962Wandel 227 130 XR comprising r 3,056,964 10/1962 Beckman et al. 227130XRa housing having means defining first and second ax1a1- 3,084,672 4/1963Dalton 7 XR y aligned cylindrical chambers, 3,094,043 6/1963 Powers etal. said first chamber being of a size greater than said 3,278,10610/1966 Becht et aL 227 8 second chambe a soil'imllnicfltingat one end3,313,213 4/1967 Wandel. thereof w1th one end of said second chamber, apiston assembly having axially spaced first and sec- TRAVIS S, M G p iExaminer ond piston heads mounted within said first and secondcylindrical chambers, respectively, for axial re- US. Cl. X.R.ciprocating movement, 227-

